Probability Map (Total Deviation)

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This image type converts total deviation (defect depth) into a symbol. The symbol represents the probability that the deviation is accidental.

P >= 5,0 %

P < 5,0 %

P < 2,0 %

P < 1,0 %

P < 0,5 %

The percentage is the probability of a deviation by chance. The smaller the figure, the less likely the deviation is accidental and the more likely is a true defect. Accordingly, the symbol gets darker. The calculation considers the different spread of normal values at different measurement points and age classes.


Probability maps are based on total deviation values   -- Click here for more information about this value type, the meaning and interpretation


CONCLUSION: This image type visualizes defects. The symbol expresses the probability of a true defect. The importance of singular defects can be recognized exactly. For a complete evaluation the Color Defect Map is needed.


Further information

Deep defects always appear with the darkest symbol     The exact depth is not indicated and can be very different. In severely damaged areas, the topography of the damage is invisible. In the follow-up, the improvement or deterioration of deeper defects is not recognizable.

In case of a homogeneous damage (cataract, small pupil) with equal defect depth values in the entire visual field, the defect probability is higher in the center (due to the smaller normal range). The map shows a false central defect.

The analysis is only related to single points. Slight reduction of sensitivity in neighboring points which are not accidental and appear as larger area in a dark green or brown in the Color Defect Map, are invisible in the Probability Plot.


Synonym: Defect Probability

The total deviation defect probability is an additional analysis of the total deviation values (defect depth values). The defect depth is statistically analyzed whether the deviation from normal is probable or the deviation is more likely to be accidental. There are several classes of defect probability:

The percentage is the probability of a deviation by chance. The smaller the figure, the less likely is a chance and the more likely is a true defect. Accordingly, the symbol gets darker.

Note: The spread of normal value is different for different visual field locations and age classes. The same total deviation value can have different defect probability classes depending on age and location.

See also: Pattern Defect Probability in the

Medical utility

The defect depth values are the real measurement results after concerning the age-corrected normal values. They abolish the exact evaluation of the defect depth.

The probability analysis improves the information power of defect depth further more.

The symbols are graphical and allow a quick evaluation of the entire visual field.

Misinterpretation

The analysis is only related to single points. Slight reduction of sensitivity in neighboring points which are not accidental and appear as larger area in a dark green or brown in the Color Defect Map, are invisible in the Total Deviation Probability Plot.

Deep defects always appear with the darkest symbol   , even when the depth is very different. In severely damaged areas, the topography of the damage is invisible. In the follow-up, the improvement or deterioration of deeper defects is not recognizable.

In case of a homogeneous damage (cataract, small pupil) with equal defect depth values in the entire visual field, the defect probability is higher in the center (due to the smaller normal range). The map shows a false central defect.

The expert says:

The defect probability map is highly suitable for the evaluation of small, localized defects.

For complete evaluation, use always the total deviation value plot and/or the Color Defect Map plus.